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Losses And Loss Adjustment Expenses (Narrative) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Extraordinary Item [Line Items] |  |  |
Decrease in provision for insured events | $ 3,000,000 mcy_DecreaseInProvisionForInsuredEvents |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years | 3,193,000 us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears | 2,960,000 us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears | 42,332,000 us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears
Increase in provision for insured events |  |  | 42,000,000 mcy_IncreaseInProvisionForInsuredEvents
Catastrophe [Member] |  |  |
Extraordinary Item [Line Items] |  |  |
Pre-tax catastrophe losses | $ 11,000,000 us-gaap_LiabilityForCatastropheClaimsCarryingAmount / us-gaap_ExtraordinaryItemAxis = us-gaap_CatastropheMember | $ 17,000,000 us-gaap_LiabilityForCatastropheClaimsCarryingAmount / us-gaap_ExtraordinaryItemAxis = us-gaap_CatastropheMember | $ 39,000,000 us-gaap_LiabilityForCatastropheClaimsCarryingAmount / us-gaap_ExtraordinaryItemAxis = us-gaap_CatastropheMember

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- Definition Decrease in provision for insured events. + References No definition available. + Details
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- Definition Increase In Provision For Insured Events. + References No definition available. + Details
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- Definition The amount of estimated liability as of the balance sheet date for the specific conflagration, earthquake, windstorm, explosion, or similar event. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
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- Definition Amount of provision in the period for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Financial Reporting Release (FRR) -Number 403 -Paragraph 04 -Subparagraph b Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
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